Silencer



g,ss2,993

K. T. MURTY April 21, 1959 SILENCER Filed Feb. 16, 1955 INVENTOR. Kenneth C Murty AGENT United States Patent Office SILENCER Kenneth T. Murty, Arlington, Tex., assignor to Chance Vought Aircraft, Incorporated, Dallas, Tex., a corporation of Delaware Application February 16, 1955, Serial No. 488,657 Claims. (Cl. 181-69) This invention relates to a new silencer in an air conduit, particularly to a more efficient silencer for reducing the acoustical noise level in a high velocity air conditioning and ventilating system.

While my silencer is designed particularly for use in air conditioning systems, it may be utilized for reducing the noises caused by internal combustion jet or reciprocating engine exhaust gases, steam, air, vapors, or the like compressible fluids in its movement at high velocity through a conduit.

My high acoustical noise silencer is particularly adaptable for utilization in air conditioning and distribution systems having an air conditioning system temperature control valve for metering the supplies of hot air and cold air, and in which the air to be metered requires and has such a high velocity i.e., subsonic to sonic speeds, as to produce a high, objectionable acoustical noise level. One of these sources of supply of high velocity air is the engine air compressor, for example.

This high noise level may result when the temperature control valve on one of the supplies of air is opened to admit the air, causing a sonic or subsonic jet of air due to the super-critical pressure ratio across the valve orifice. The present mufllers as in U.S. 2,122,447, for example, have proven to be insufficient in attempting to control this near sonic speed air jet noise because they are basically built for low frequency muflling of pulsing type airflows instead of for the higher frequency noise originating from a subsonic to supersonic jet of air. When this jet of air in the near sonic velocity zone extends into the present mufliers, apparently high local velocities are produced preventing the mufller from efficiently silencing the noise. I have found that the excessive noise from the air conduit may be diminished by proper control of the expansion of air downstream of the control valve.

Accordingly, the principal object of my invention is to construct a mechanism that provides proper control of the expansion of a compressible fluid in a conduit wherein the acoustical noise level is reduced to a nonobjectionable level.

Another object of my invention is to provide an efficient silencer for compressible fluids traveling at from subsonic to supersonic velocities.

Another object of my invention is to provide a more efficient, lighter in weight, durable, and inexpensive to manufacture silencer for reducing the acoustical noise level in a compressible fluid conduit.

Yet another object of my invention is to provide a silencer that may be readily adapted in present air conditioning and ventilating systems.

Other objects and advantages of the invention will be apparent from the following detailed description, together with the accompanying drawings, submitted for purposes of illustration only and not intended to define the scope of the invention, reference being bad for that purpose to the subjoined claims.

2,882,993 Patented Apr. 21, 1959 In the drawings:

Fig. l is a schematic illustration of an air conditioning and ventilating system incorporating the new silencer; and

Fig. 2 is a detailed perspective view of the new silencer with parts cut away for clarity of disclosure illustrating the first and last orifice plates.

My new silencer 10 is illustrated schematically in Fig. 1 as it may be incorporated in an air conditioning and ventilating system wherein a sonic, near sonic or subsonic jet of air is created in the air conduit such as, but not limited to that used in high speed aircraft. Fig. 1 illustrates one system, for example, comprising a cold air butterfly metering valve 11, cold air conduit 12, air conditioning turbine 13, emergency ventilation air conduit 14, hot air butterfly metering valve 15, hot air conduit 16, silencer 10, and conduit 17 adapted to connect to an aircraft cabin or the like. For additional silencing, a muffler may be incorporated in the cabin conduit 17 be low the mixing area of the cold and hot air, if so desired.

The schematic showing of silencer 10 in Fig. l merely illustrates the feature of increased orifice area of each downstream orifice plate to provide expansion of the "hot air downstream of the hot-air valve.

The novel silencer 10, Fig. 2, provides for expansion and mixing of the high velocity air i.e., usually air above Mach number of .6, so that the acoustical noise level is lowered considerably to below decibels to an allowable, non-objectionable level. The acoustical noise level may become very objectionable in the transonic speed range, i.e., velocities in the Mach number range of 0.75 M l.20 as defined in Airplane Aerodynamics by D. O. Domasch, S. S. Sherby, and T. F. Connolly, 1951. Accordingly the noise level of the jet air becomes objectionable beginning in the low range of transo-nic speeds, i.e., Mach numbers of from 0.75 to 1.0, and becomes Worse with increase in speed. The orifice plate 18a-18f of the disclosed invention are secured internally of the walls of the silencer and coaxial with the silencer longitudinal axis by having the peripheral edges of the plates secured to the wall surfaces, as by welding or the like. In hot air conduit 16, the first orifice plate 18a downstream of the hot air metering control valve 15 has a few, small orifices and with each succeeding orifice plate downstream in the high velocity air conduit, the total area of the orifices or openings increases. To provide a constant increase in orifice area from the first entering plate, as plate 18a, to the last plate 18] through which the air passes during its expansion, the size of some openings, the number of others, or both the size and number in others are increased in each succeeding plate downstream. Accordingly, the porosity of the plate increases in the downstream direction. In one successful version of the disclosed silencer 10 for example, six substantially equally spaced orifice plates 18a18,f are utilized in a two and one half inch conduit 16, the ori fices 19a-19f varying from six to ten substantially equally spaced one eighth inch openings 19a in the first plate 18a to between eighteen and twenty-four equally spaced one quarter inch holes 19 in the last plate 18]. Obviously, for compressible fluid conduits of other sizes the number and size of the orifices may be varied accordingly to provide the proper control of the fluid expansion in the conduit to reduce the acoustical noise level to a lower and non-objectionable level.

A further feature of this invention resolves in the construction of the silencer wherein the plates may be secured in a curved portion of the conduit instead of the straight portion illustrated. While the silencer 10 is illustrated as an integral portion of conduit 16, it may be constructed as a separate section of conduit if so desired. And still further, the silencer may be of greater diameter than its adjoining upstream conduit, as illustrated, for improved control of the expansion of the compressible fluid.

Test results have shown that no low speed, straight through type of muffler and particularly, one as shown in Patent No. 2,548,563, of a practical size could reduce sonic air conditioning noises to a satisfactory value. The silencer of the present invention, which has a multiplicity of orifices in a plurality of spaced plates in the hot air conduit, readily diminishes the sonic air noise to a satisfactory level. The present invention provides a simple, lightweight, inexpensive, and easy to manufacture silencer that alleviates the problem of high acoustical noises due to a jet of air in the subsonic to higher speed range.

In operation, cold air is furnished to the cabin air supply conduit 17 by cold air metering valve 11 and via conduit 12 and turbine 13. Hot air is supplied to the cabin air supply conduit 17 via hot air metering valve and conduit 16. Where the air of the air supply, as the hot air supply in my case, may have subsonic to supersonic velocities and produce an unduly high noise level, i.e,, above at least 100 decibels, this excessive noise is attenuated by passing it through silencer 10 in the hot air conduit 16. While various types of air conditioning temperature control valves may be utilized, the instant disclosure comprises hot and cold air valves 15 and 11 mounted coaxially on a rod at an angle radially with each other. The air conditioning temperature control valve is formed for metering the proper amounts of hot and cold air to provide a mixture at the desired temperature. An alternate and additional air conduit 14 may be provided for emergency supply.

It will be obvious to those skilled in the art that various changes may be made in the invention without departing from the spirit and scope thereof and therefore the invention is not limited by that which is shown in the drawings and described in the specification, but only as indicated in the appended claims.

Iclaim:

1. In an air conditioning system having .a jet of air near sonic velocity in a fluid flow conduit, a silencer comprising, a housing consisting of a tubular part of the fluid flow conduit receiving the jet of air, substantially parallel equally spaced flat plates normal to the conduit longitudinal axis and having their peripheral edges secured to the conduit internal walls, said plates being in immediate consecutive order, the first of said flat plates receiving the near sonic velocity air jet having a plurality of substantially equally spaced orifices of equal size therein, and each plate having orifices therein which are larger in number and in size than those of the preceding plate upstream thereof to reduce the acoustical noise level in the air conditioning system.

2. A silencer for reducing the high acoustical noise level in an air conditioning system due to the air in a conduit thereof having at least a transonic velocity comprising, substantially parallel equally spaced apart flat plates coaxial wtih the conduit longitudinal axis for encountering the transonic air, each of said flat plates having a plurality of substantially equally spaced and sized orifices therein, the number and size of said orifices in each plate being greater than that of the preceding plate upstream thereof, said plates being in immediate consecutive order and extending to the internal wall of the conduit.

3. A silencer for reducing the high acoustical noise level in a conduit due to the air therein having at least a transonic velocity comprising, substantially parallel and equally spaced apart flat plates coaxial with the conduit longitudinal axis for incurring the transonic air, each of said flat plates having a plurality of substantially equally spaced and sized orifices therein, the number and size of said orifices in each plate being greater than that of the preceding plate upstream thereof, said plates being in immediate consecutive order and extending to the internal wall of the conduit.

4. A silencer for reducing the high acoustical noise level in a conduit due to the air therein having at least a transonic velocity comprising, equally spaced apart flat plates coaxial with the conduit longitudinal axis for encountering the transonic air, each of said flat plates having a plurality of substantially equally spaced and sized orifices therein, the number and size of said orifices in each plate being greater than that of the preceding plate upstream thereof, said plates being in immediate consecutive order and extending to the internal wall of the conduit.

5. A silencer for reducing the high acoustical noise level in a conduit due to the compressible fluid therein having at least a transonic velocity comprising, equally spaced apart plates for encountering the transonic fluid, each of said plates having a plurality of substantially equally spaced and sized orifices therein, the number and size of said orifices in each plate being greater than that of the preceding plate upstream thereof, said plates being plates for encountering the transonic fluid, each of said 1 plates having a plurality of substantially equally spaced and sized orifices therein, the number of said orifice in each plate being greater than that of the preceding plate upstream thereof, said plates being in immediate consecutive order and extending to the internal wall of the conduit.

7. A silencer for reducing the high acoustical noise level in a conduit having a jet of compressible fluid of at least transonic velocity comprising, equally spaced apart plates for encountering the transonic fluid, each of said plates having a plurality of substantially equally spaced and sized orifices therein, the size of said orifices in each plate being greater than that of the preceding plate up-' stream thereof, said plates being in immediate consecutive order .and extending to the internal wall of the conduit.

8. A silencer for reducing the high acoustical noise level in a conduit having a jet of compressible fluid at least in the low range of transonic velocity comprising, equally spaced apart plates secured transversely in a portion of the conduit for encountering the transonic fluid, each of said plates having substantially equally spaced orifices therein, the number of said orifices in each plate being greater than that of the preceding plate upstream thereof, said plates being in immediate consecutive order and extending to the internal wall of the conduit.

9. A silencer for reducing the high acoustical noise level in a conduit having a jet of compressible fluid at least in the low range of transonic velocity comprising, equally spaced apart plates secured transversely in a portion of the conduit for encountering the transonic fluid, each of said plates having substantially equal sized orifices therein, the size of said orifices in each plate being greater than that of the preceding plate upstream thereof, said plates being in immediate consecutive order and extending to the internal wall of the conduit.

10. In a system of the class described having therein a jet of air of at least transonic velocity, a silencer in the system adjacent to and downstream of the jet of air, said silencer having equally spaced apart perforated plates for encountering the jet of :air of at least transonic velocity, the porosity of each of said plates being greater than the adjacent upstream plate, said plates being in immediate consecutive order and extending to the internal wall of 1,186,067

the conduit. 2,007,153

References Cited in the file of this patent 2,5485 63 UNITED STATES PATENTS 5 213,348 Richardson Mar. 18, 1879 327,933

'6 Becker June 6, 1916 Boggs July 9, 1935 Tyden Mar. 30, 1937 Smith Apr. 10, 1951 FOREIGN PATENTS France Apr. 22, 1903 

